I had this too. It turned out in my case that this is an issue mentioned in the CentOS 5.6 release notes, where a manual change I had previously had to make to /usr/sbin/vmware-hostd to get VMware Server to work under CentOS 5.4/5.5 had to be removed again to get it to work under 5.6.

If you have a line like "export LD_LIBRARY_PATH" at the end of vmware-hostd, comment it out again and you may find everything just works again.